Potent Storm System to Impact Central US

 Potent Storm to Impact the Central US tonight through Saturday 

Aidan Cera 

A powerful storm system is expected to track across the central United States beginning overnight tonight lasting through mid day on Saturday. All modes of weather are possible from blizzard like conditions to tornados across the upper Midwest tonight through Saturday morning. 

Tonight

           Figure 1. NAM-3km frontogenesis output initiated 00Z 03/31/23 through 12Z 03/31/23

Warm air advection is expected to advance northward overnight tonight across Iowa, Wisconsin and Minnesota along a warm front. This warm front will be the initial focus point for continued for a variety of precipitation across this region ranging from snow in Minnesota and northern Wisconsin to thunderstorms in southern Minnesota, Wisconsin and throughout Iowa.

 

Figure 2. HRRR-1km Res 00Z Reflectivity run spanning from 00Z to 12Z 03/31/23.

As the warm front pushes north and stalls somewheres across northern Iowa overnight, precipitation coverage is expected to increase thanks to continual moisture transport northward. The main precipitation mode for Iowa, southern and central Wisconsin and southern Minnesota looks to be rain given the warm temperature transport northward along and ahead of the warm front itself. There even is the potential for some thunderstorm development across southern Minnesota and Iowa as instability works its way north with the warm front . Precipitation mode looks to become more messy once you get north of US Highway 8 in western and central Wisconsin, north of the Twin Cities metro and areas north of I-94 in Minnesota. Temperatures are expected to be hover near the freezing mark in areas where precipitation is already falling due to evaporative cooling. This will lead to a rain/snow mix in some areas or freezing rain in others due to a slightly warmer 850 mb layer aloft. Ice accumulation on roadways is expected ranging from 0.1" to 0.25" of ice accumulation. This will likely lead to difficult driving conditions especially on roads not treated or used as well so take extreme caution when driving anywhere. A winter weather advisory is in place for much of Minnesota and northern Wisconsin with concerns for icy driving conditions and will remain in effect for most areas until at least 10AM CST Friday. 

Figure 3. NWS Twin Cities Ice Accumulation Graphic with Ice accumulation totals and counties under a Winter Weather Advisory.

Friday 

Friday looks to feature a wide assortment of inclimate weather across Minnesota, Wisconsin and Iowa to say the least. Everything from blizzard like conditions to severe thunderstorms is expected across the upper Midwest. There are a lot of elements to this forecast so here we go....

Figure 3. WPC expected weather conditions for Friday 03/31/23

Minnesota and Northern Wisconsin (the wintry side)

A messy wintry mix is expected to continue across central Minnesota through northern Wisconsin Friday morning north of the warm front. Heading into the late morning things look to calm down somewhat across central Minnesota, central and southern Wisconsin and most of Iowa. As the morning leads to the afternoon, we are expecting to see the surface low track out of Nebraska and into Iowa, with a building snow band draped across South Dakota. Ample forcing associated with strong positive vorticity advection accompanying the low and tight pressure and moisture gradient to the south will lead to the low to quickly deepend and advect northeastward bringing heavy snow into western Minnesota by late afternoon then central Minnesota by sun down. 

Winds will pick up dramatically while the low passes us to the south due to a strong pressure gradient in concurrence with the snow beginning to fall which will lead to a significant blowing snow hazard and reduced visibility. The NWS has issued Blizzard Warnings for portions of southwestern Minnesota in anticipation of near white out conditions and almost impossible travel conditions. 

Figure 5. NWS advisories and warnings issues. Purple indicates Winter Weather Advisory, pink Winter Storm Warning and red Blizzard Warnings. 

Figure 6. NWS expected snow accumulation for Minnesota and western Wisconsin.

In terms of snow accumulations, it will truly depend a lot of where the heavily forced band of snow will develop on the north side of the low. This of course depends on the track of the low and how far north or south it ends up tracking. Therefore snow totals vary quite substantially as well. There are some models that show central Minnesota getting missed entirely, and while I think this may be a bit far fetched, there is a slim possibility that parts of Minnesota are spared of the worst of these conditions but this is not an assumption that I would feel safe putting any money on. Most of central Minnesota should expect at least a couple inches of snow with the higher end being just over a foot. Heavier accumulations should be anticipated from the Twin Cities metro eastward to Eau Claire and area north of Wisconsin Highway 29 due to stronger forcing with the low across this region and more moisture to work with later Friday night. 

The bottom line is regardless of the snowfall amounts, roads will be hazardous to drive on given the freezing rain expected across much of the area tonight and then the snow and heavy winds tomorrow afternoon through Saturday morning. Anyone who has plans to travel should either adjust their plans if possible or take extreme caution when driving.

Iowa and southern Wisconsin (Severe Wx)

Figure 7. SPC categorical severe thunderstorm outlook for Friday 03/31/23 

While Minnesota and northern Wisconsin will be dealing with heavy snow and other various forms of wintry precipitation, Iowa, southern Wisconsin and northern Illinois are under a moderate risk of severe thunderstorms with all modes of severe weather possible including damaging winds, large hail and strong tornados. 

Figure 8. NAM-3km 850 hPa Temp, Temp Advection, Frontogenesis and wind for Friday morning through Friday night. 

A powerful cold front is expected to develop across eastern Nebraska and Kansas early Friday afternoon. Strong cold air advection and frontogenesis quickly build along the front as it tracks across Iowa and Missouri then into Wisconsin and Illinois. Given the strong vertical forcing, ample deep layer shear and instability, strong thunderstorms are expected to initiate across central Iowa around 3-4 PM CST and quickly move eastward. Prefrontal thunderstorm development is also expected across eastern Iowa, southern Wisconsin and northern Illinois. This activity is expected to maintain a more classic cellular mode for a longer period of time then the storms along the cold front due to the nature of the wind shear ahead of the cold front.

Hodographs show veering winds across eastern Iowa, southern Wisconsin and northwestern Illinois tomorrow afternoon. Models also show CAPE values of between 1,000 to 2,000 J/kg which is plenty of instability to maintain long lived severe type of thunderstorms. 

With all of this considered, there is a substantial risk for strong, long track tornadoes across eastern Iowa and northwestern Illinois tomorrow late afternoon and evening with any discrete cells that are able to maintain themselves. 

Significant hail will also be possible across eastern Iowa due to steep lapse rates and some modest mid level dry air aloft. 

As the evening progresses, the cold front will quickly catch up to any prefrontal thunderstorm development and a Quasi-Linear Convective System (QLCS) is expected to develop across eastern Iowa and Missouri and track eastward into southern Wisconsin and Illinois. Damaging winds will become the primary threat with these storms, but a few embedded tornados, some of which could be strong, can certainly not be ruled out.

Something to note is that some of these thunderstorms may make it into extreme southeastern Minnesota Friday afternoon into the evening, and while conditions are not as favorable for severe weather modes as they will be down in Iowa, some mid level instability is expected to be present. Given this, a few stronger thunderstorms with some gusty winds and perhaps even some hail cannot be ruled out for Minnesota's extreme southeast counties. 

Figure 9. HRRR reflectivity output for Friday afternoon into the overnight hours.

Figure 10. NAM-3km reflectivity output for Friday afternoon into the overnight hours. 

The SPC has issued moderate probabilities for all modes of severe weather for this event as shown below.

Figure 11. SPC tornado probabilities for Friday 03/31/23.

Figure 12. SPC damaging wind probabilities for 03/31/23.

Figure 13. SPC large hail probabilities for 03/31/23.

Overall, tomorrow is going to be an extremely busy day across the upper Midwest as a classic spring storm makes it's way out of the Rocky Mountains tonight and into the Plains tomorrow. Regardless of what weather you are expecting be it snow, rain or severe thunderstorms, it will be very important to remain weather aware so that you can make the best possible decisions with regards to handling whatever the weather may throw your way. 

For more information please consult your local NWS office, be it NWS Twin Cities, La Crosse, Sioux Falls, Des Moines or Davenport.